Residues at the subunit interfaces of the nicotinic acetylcholine receptor that contribute to alpha-conotoxin M1 binding

The two binding sites in the pentameric nicotinic acetylcholine receptor of subunit composition alpha2 beta gamma delta are formed by nonequivalent alpha-gamma and alpha-delta subunit interfaces, which produce site selectivity in the binding of agonists and antagonists. We show by sedimentation analysis that 125I-alpha-conotoxin M1 binds with high affinity to the alpha-delta subunit dimers, but not to alpha-gamma dimers, nor to alpha, gamma, and delta monomers, a finding consistent with alpha-conotoxin M1 selectivity for the alpha delta interface in the intact receptor measured by competition against alpha-bungarotoxin binding. We also extend previous identification of alpha-conotoxin M1 determinants in the gamma and delta subunits to the alpha subunit interface by mutagenesis of conserved residues in the alpha subunit. Most mutations of the alpha subunit affect affinity similarly at the two sites, but Tyr93Phe, Val188Lys, Tyr190Thr, Tyr198Thr, and Asp152Asn affect affinity in a site-selective manner. Mutant cycle analysis reveals only weak or no interactions between mutant alpha and non-alpha subunits, indicating that side chains of the alpha subunit do not interact with those of the gamma or delta subunits in stabilizing alpha-conotoxin M1. The overall findings suggest different binding configurations of alpha-conotoxin M1 at the alpha-delta and alpha-gamma binding interfaces.

Toxins selective for subunit interfaces as probes of nicotinic acetylcholine receptor structure

The pentameric structure of the nicotinic acetylcholine receptor with two of the five subunit interfaces serving as ligand binding sites offers an opportunity to distinguish features on the surfaces of the subunits and their ligand specificity characteristics. This problem has been approached through the study of assembly of subunits and binding characteristics of selective peptide toxins. The receptor, with its circular order of homologous subunits (alpha gamma alpha delta beta), assembles in only one arrangement, and through mutagenesis, the residues governing assembly can be ascertained. Selectivity of certain toxins is sufficient to readily distinguish between sites at the alpha gamma and alpha delta interfaces. By interchanging residues on the gamma and delta subunits, and ascertaining how they interact with the alpha-subunit, determinants forming the binding sites can be delineated. The alpha-conotoxins, which contain two disulfide loops and 12-14 amino acids, show a 10,000-fold preference for the alpha delta over the alpha gamma subunit interface with alpha epsilon falling between the two. The waglerins, as 22-24 amino acid peptides with a single core disulfide loop, show a 2000-fold preference for alpha epsilon over the alpha gamma and alpha delta interfaces. Finally, the 6700 Da short alpha-neurotoxin from N. mossambica mossambica shows a 10,000-fold preference for the alpha gamma and alpha delta interfaces over alpha epsilon. Selective mutagenesis enables one to also distinguish alpha-neurotoxin binding at the alpha gamma and alpha delta subunits. This information, when coupled with homology modeling of domains and site-directed residue modification, reveals important elements of receptor structure and conformation.

Pancreatic exocrine dysfunction associated with mitochondrial tRNA(Leu)(UUR) mutation

We report on pancreatic exocrine dysfunction in families that have the mitochondrial tRNA(Leu)(UUR) gene mutation. These families exhibited maternally inherited diabetes mellitus (DM) and an A to G substitution at nt 3243 of the mitochondrial tRNA(Leu)(UUR) gene (A3243G mutation). Pancreatic necropsy samples from one proband showed accumulation of degenerated mitochondria in pancreatic acinar cells. Pancreatic exocrine dysfunction was recognised by a functional pancreatic study. This study indicates that exocrine pancreatic dysfunction may be associated with the A3243G mutation.

[Analysis of postoperative shivering following the deliberate mild hypothermia during neurosurgery]

We induced deliberate mild hypothermia in 96 patients who underwent intracranial operations using a water blanket and a convective device blanket. The lowest temperature measured at the tympanic membrane during mild hypothermia was adjusted to 34.5 degrees C. The patients were divided into two groups in respect to the occurrence of postoperative shivering, and the relationship between the perioperative parameters and the occurrence of postoperative shivering was evaluated. Shivering was observed postoperatively in 29 to 96 patients (30.2%). In the group with shivering (SV), age was significantly lower and body weight and body surface area were significantly larger than the group without shivering (NSV). Urinary output was significantly larger in SV than in NSV. Tympanic membrane, nasopharyngeal, and rectal temperatures at the end of surgery and nasopharyngeal, rectal, and peripheral temperatures just after the extubation were significantly lower in SV than in NSV. These results suggest that sufficient rewarming of both the core and peripheral temperatures is important to prevent the postoperative shivering following the mild hypothermic therapy in neurosurgical patients, especially in young patients.

Probucol treatment attenuates the aortic atherosclerosis in Watanabe heritable hyperlipidemic rabbits

We examined the effect of probucol on the aortic atherosclerosis already developed in Watanabe heritable hyperlipidemic (WHHL) rabbits at the initiation of treatment. In WHHL rabbits treated with probucol for 5 months from 8 months old, the lesion area in the aorta was significantly (P < 0.05) reduced when compared with that in untreated animals as well as animals at age 8 months. In contrast, plasma cholesterol levels in the probucol-treated group and untreated group during the experiment were not significantly different. LDL prepared from rabbits receiving probucol for 5 months showed resistance to oxidation by copper ions. Plasma CETP activity was significantly (P < 0.05) increased by probucol treatment. An immunohistochemical study showed that macrophages were abundant in the atherosclerotic lesions of untreated rabbits whereas smooth muscle cells were predominant in lesions of probucol-treated rabbits. These results suggest that the atherosclerotic lesion in WHHL rabbits can regress when treated by probucol and that the attenuation of atherosclerosis in this animal involves effects of probucol other than a decrease in plasma cholesterol, for example anti-oxidant activity.

Dried green leaf powders of Jew's mellow (Corchorus), persimmon (Diosphyros kaki) and sweet potato (Ipomoea batatas poir) lower hepatic cholesterol concentration and increase fecal bile acid excretion in rats fed a cholesterol-free diet

A cholesterol-free diet containing dried powder of Jew's mellow leaves, persimmon leaves or sweet potato leaves respectively at 5% level as dietary fiber was fed to male Sprague-Dawley rats for about one month. The experiment was conducted twice except for sweet potato leaves. In the groups fed the diet mixed with powders of any of the three different dried green leaves, the hepatic cholesterol concentration significantly decreased. Such lowering was not observed in serum cholesterol concentration compared with the control (cellulose) group. A significant increase in fecal weight was observed in all the groups fed the green leaf samples. All the dried green leaves increased fecal excretion of bile acids per gram or per day compared with the control group in both experiments, but only the dried Jew's mellow leaves showed an increased excretion of neutral sterols. These results suggest that lowering of hepatic cholesterol by powdered green leaves is not necessarily due to the same factor, but to the increased fecal excretion of bile acids due to inhibited enterohepatic circulation in animals given these samples.

[Low-dose levodopa therapy of autistic disorder: evaluation of clinical effectiveness]

Based upon the hypothesis that brain monoamine metabolism is disorganized in some children with an autistic disorder, we tried low dose levodopa therapy (0.5 mg/kg/day) proposed by Segawa, et al. We treated 20 patients with an autistic disorder diagnosed according to DSM-IV, and evaluated the effectiveness. A double blind cross over method was applied in this study because of the small number of patients. Drug effects were observed carefully by the psychologists and pediatric neurologists using an evaluation sheet consisting of twenty items. No significant effectiveness was observed in this study, although four cases (20%) showed some improvement. In conclusion, administration of low dose levodopa to autistic children resulted in no clear clinical improvements of autistic symptoms.

Neuroleptic malignant syndrome and hydroxylase gene mutations: no association with CYP2D6A or CYP2D6B

To examine a possible association between debrisoquine 4-hydroxylase gene mutations and neuroleptic malignant syndrome, we assessed frequencies of wild type and A and B mutant alleles of the CYP2D6 gene in 24 patients with a history of neuroleptic malignant syndrome, 50 patients with neuroleptic-treated schizophrenia but no history of neuroleptic malignant syndrome, and 50 healthy controls. Allele frequencies did not differ significantly between these groups. Homozygotes for CYP2D6A and for CYP2D6B, which indicate a poor-metabolizer phenotype for the CYP2D6 substrate, were not detected among the neuroleptic malignant syndrome cases. This result indicates no excess of poor CYP2D6 metabolizers in neuroleptic malignant syndrome. The aetiology of neuroleptic malignant syndrome is not explainable in terms of CYP2D6 gene mutations.

Eye-tracking device comparisons of three methods of magnetic resonance image series displays

This study evaluated the effectiveness of three kinds of display methods for magnetic resonance (MR) image interpretation using an eye-tracking device. Seven radiologists interpreted head MR studies by using a single monitor (17-inch, 1,024 X 1,280 bit) in the 4 images/screen display format. Three paging modes were compared: (A) rapid paging only, (B) multiple image series display at the same slice position with consecutive rapid paging, and (C) simultaneous display of multiple series with each image series being browsed independently. Using an eye-mark camera, the radiologist's point of fixation and the duration of fixation were recorded during actual image interpretation. In mode A, the duration of fixation was short, and the points of fixation were distributed randomly over the visual field. In mode B, the points of fixation were clustered chiefly on a specific image series. In mode C, the points of fixation were not clustered on a specified series, but the duration of viewing the T2 series was relatively long. The total tracing area in mode B and C was smaller than that in mode A. Multiple series display, in which selected key series of slices could be viewed effectively, was found to be suitable for MR image interpretation.

Immortalized gastric epithelial cell line GSM06 synthesizes hyaluronan under the influence of simian virus 40 large T-antigen expression

GSM06 is a cell line established from the stomach of transgenic mouse harboring a temperature-sensitive simian virus 40 (SV40) large T-antigen gene. 3H-labeled macromolecules produced by the cells incubated with [3H] glucosamine were characterized to examine whether or not GSM06 cells synthesize mucin (mucus glycoprotein). The GSM06 cells grew until a confluent monolayer formed at 33 degrees C (the permissive temperature for SV40 large T-antigen expression), and the 3H-labeled macromolecules appeared in both cell extract and medium during culture for at least 1 week. Unexpectedly, almost all 3H-labeled macromolecules, which were excluded from a column of Sepharose CL-4B, were identified as hyaluronan by analyses using Sepharose CL-2B chromatography, cesium trifluoroacetate equilibrium centrifugation, treatment with dithiothreitol, and trypsin, hyaluronidase, and chondroitinase ABC digestion. At a nonpermissive temperature (39 degrees C), GSM06 cells grew only slightly, but produced much more hyaluronan than at 33 degrees C. The results indicate that GSM06 cells produce not mucin, but hyaluronan, and that the expression of large T-antigen may influence hyaluronan synthesis in GSM06 cells.

A model of the nicotinic receptor extracellular domain based on sequence identity and residue location

We have modeled the extracellular domains of individual subunits (amino acids 31-200) in the nicotinic acetylcholine receptor using sequence homology with copper binding proteins of known crystal structure, plastocyanin and pseudoazurin, and data from recent site-specific mutagenesis, antibody mapping, and site-directed labelling studies. These data formed an initial model that was refined using molecular dynamics and mechanics as well as electrostatic and solvation energy calculations. The sequences between residues 31 and 164 in the alpha 1-subunit and corresponding residues in homologous receptor subunits show similarity with the core sequence of the cation binding site in plastocyanin and pseudoazurin, a region in the template proteins characterized by multiple hairpin loops. In addition to defining the subunit interfaces that comprise the site for agonist and competitive antagonist binding in more detail, the findings show that negatively charged residues cluster in domains arranged to diminish electrostatic free energy of the complex. Electrostatic factors also appear to distinguish the ligand binding interfaces, alpha gamma and alpha delta, from the other three interfaces on the pentameric receptor.

6-Pyruvoyl-tetrahydropterin synthase deficiency with generalized dystonia and diurnal fluctuation of symptoms: a clinical and molecular study

We report the case of a 44-year-old woman with a partial 6-pyruvoyl tetrahydropterin synthase (6-PTS) deficiency, whose predominant clinical symptom was generalized dystonia with marked diurnal fluctuation. Dystonia was present in the eyelids, oromandibular region, trunk, and extremities (Meige syndrome plus double hemiplegia-like dystonia). A marked and sustained positive response to levodopa was observed. A molecular genetic study revealed a homozygous mutation (I114V) in the 6-PTS gene. This study indicates that genetic abnormality in the 6-PTS gene may be a hereditary dystonia disorder. We speculate that our patient has residual 6-PTS activity in the central nervous system, such as in the liver, and we suggest that residual, but insufficient production of tetrahydrobiopterin may play an important role in causing diurnal fluctuation of symptoms.

[Highly reproducible technique for the estimation of trabecular bone density: three slice method on peripheral quantitative CT]

The reproducibility of bone mineral density (BMD) measurements with peripheral quantitative CT has been limited by the repositioning error. In this study, 1 mm-step 3-slice scan data were used to compensate for this error in trabecular BMD of the distal radius. The assessment was based on the liner relations between the cross-sectional area and trabecular bone mineral content and trabecular area ratio, on the condition that the trabecular bone is defined by a BMD value. The estimated reproducible errors of less than 2% under clinical conditions indicate that the method is reliable for follow-up examination.

Proprotein-processing endoprotease furin controls the growth and differentiation of gastric surface mucous cells

Gastric surface mucous cells originate from progenitor cells at the isthmus of the gastric gland, from where the cells migrate to the luminal surface. With migration they form secretory granules and express TGF alpha. We found that proprotein-processing endoprotease furin-positive cells were layered around the upper one fourth of the gastric glands of adult rats, whereas they were distributed along an outer epithelial layer in fetal rats. Because the furin-positive cell layer was localized from the upper cell proliferating zone to the less proliferating pit-cell region in the gastric gland unit, we examined the role of furin in the growth and differentiation of surface mucous cells by using the cell line, GSM06. This cell line is derived from the gastric surface mucous cells of transgenic mice harboring the temperature-sensitive simian virus 40 T antigen. At T antigen-active temperature (33 degrees C), the cells grew to confluency, whereas at T antigen-inactive temperature (39 degrees C), the cells ceased growing. At 33 degrees C, the cells exhibited a high level of furin expression with a negligible level of periodic acid Schiff (PAS)-positive materials and a low level of TGF alpha. In contrast, at 39 degrees C the cells produced a high level of PAS-positive materials, TGF alpha, and secretory granules, with a negligible level of furin expression. To further examine the role of furin, we established a GSM06 cell line introduced with either a sense or an antisense furin cDNA. The cells with sense furin expression produced fewer PAS-positive materials and a low level of TGF alpha even at 39 degrees C, whereas the cells with antisense furin expression exhibited more PAS-positive materials and TGF alpha even at 33 degrees C. When furin expression was suppressed by its antisense oligonucleotide, the cell growth was retarded with enhanced expression of the differentiated characteristics. Thus, we conclude that furin is instrumental in controlling the growth of the surface mucous cells.

Evaluation of the role of lactate dehydrogenase in oxalate synthesis

The kinetic properties of lactate dehydrogenase (LDH) (EC 1.1.1.27) from spinach leaves were studied in order to evaluate the possible roles of LDH in the production of oxalate. LDH was purified by affinity chromatography on affigel blue and oxamate agarose columns. The pH optimum for the reduction of pyruvate was 7.25, while that for the reduction of glyoxylate was 7. The rate of reduction of pyruvate and glyoxylate at the optimum pH indicated substrate inhibition at concentrations above 8 and 40 mM, respectively. The maximum activity of LDH with pyruvate was about three times greater than with glyoxylate. The pH optimum for the oxidation of lactate was 9, with very low activity below pH 8. Substrate inhibition was apparent at lactate concentrations above 10 mM. LDH was inactive with glyoxylate in the oxidative reaction, which would lead to the biosynthesis of oxalate.

Insulin stimulates production of glycoconjugate layers on the cell surface of gastric surface mucous cell line GSM06

The mechanism of regulation of mucus production in the gastric mucosa remains unclear. Recently, we established a gastric surface mucous cell line GSM06, which produces periodic acid-Shiff (PAS)-positive glycoconjugate (mucus) layers on the cell surface, from transgenic mice harboring a temperature-sensitive simian virus 40 large T-antigen gene. In this study, GSM06 cells were examined for its production of PAS-positive glycoconjugate layers to acid secretagogues and growth factors. The cells were cultured at nonpermissive temperature (39 degrees C) for 3-18 days and stained with PAS. Insulin (1-30 microg/ml; 0.29-8.6 microM) time- and dose-dependently increased production of glycoconjugates on the cell surface. When glycoconjugate layers produced by stimulation of insulin (3-30 microg/ml; 0.86-8.6 microM) were removed from the cell surface of GSM06 cells by a mild trypsin treatment, PAS-positive materials were remarkably decreased (day 18). In addition, morphological findings indicate that a high concentration of insulin (30 microg/ml; 8.6 microM) produced thick PAS-positive glycoconjugate layers just like normal gastric surface mucosa on the cell surface on day 18. In contrast, histamine (0.1-100 microM), carbachol (0.1-100 microM), gastrin-17 (0.1-100 nM), epidermal growth factor (0.01-10 ng/ ml; 1.7-1,700 pM), transforming growth factor-alpha (0.01-10 ng/ml; 1.8-1,800 pM), and fetal bovine serum (1-10%) did not increase glycoconjugate production. These findings suggest that insulin is a stimulator of glycoconjugate production, and stimulates production of glycoconjugate layers on the cell surface in the gastric surface mucous cell line GSM06.

Mutations in the proteolipid protein gene in Japanese families with Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease (PMD) is a rare X-linked dysmyelinating disorder of the CNS resulting from abnormalities in the proteolipid protein (PLP) gene. Exonic mutations in the PLP gene are present in 10 to 25% of all cases. In investigating genotype-phenotype correlations, we screened five Japanese families with PMD for PLP gene mutations and compared their clinical manifestations. We identified two novel nucleotide substitutions in exon 5, at V208N and at P210L, in two families. In the remaining three families, there were no mutations detected. Although all patients satisfied the criteria for the classical form of PMD, two families not carrying the mutations showed milder clinical manifestations than those with the mutations. Since linkage analysis has shown homogeneity at the PLP locus in patients with PMD, our findings suggest that there may be genetic abnormalities other than exonic mutations that cause milder forms of PMD.

Anionic residue in the alpha-subunit of the nicotinic acetylcholine receptor contributing to subunit assembly and ligand binding

To ascertain the anionic sites on the nicotinic receptor to which acetylcholine and other quaternary ammonium ligands bind, we have examined the role of an aspartyl residue (Asp-152) in the alpha-subunit. Prior photolytic labeling with agonist analogues of the neighboring residues Trp-149 and Tyr-151 suggests that their side chains reside on the binding face (also termed the (+)- or counterclockwise face) of the alpha-subunit. Asp-152 presents an anionic charge in the vicinity of these aromatic residues. Modification of the aspartate to asparagine (D152N) creates a glycosylation signal (Asn-152-Gly-Ser), and we find, on the basis of altered electrophoretic migration, that glycosylation occurs at this position upon cotransfection of the mutant alpha-subunit with beta-, gamma-, and delta-subunits. Glycosylation results in a reduction in the capacity of the receptor to assemble; this reduction is manifest in the initial step of dimer formation between the alphagamma- and alphadelta-subunits. The alpha-subunit mutant receptor reaching the assembled pentamer exhibits an altered selectivity for certain ligands. Little reduction in alpha-bungarotoxin binding is observed, whereas affinities for agonists and competitive alkaloid antagonists are reduced substantially. Separation of the contributions of charge removal and glycosylation addition shows that both factors affect agonist affinity, with the charge influence being far more predominant. These findings raise the possibility that a component of the coulombic attraction stabilizing the binding of agonists comes from the aspartyl residue at position 152 in the alpha-subunit.

A duplicated PLP gene causing Pelizaeus-Merzbacher disease detected by comparative multiplex PCR

Pelizaeus-Merzbacher disease (PMD) is an X-linked dysmyelinating disorder caused by abnormalities in the proteolipid protein (PLP) gene, which is essential for oligodendrocyte differentiation and CNS myelin formation. Although linkage analysis has shown the homogeneity at the PLP locus in patients with PMD, exonic mutations in the PLP gene have been identified in only 10%-25% of all cases, which suggests the presence of other genetic aberrations, including gene duplication. In this study, we examined five families with PMD not carrying exonic mutations in PLP gene, using comparative multiplex PCR (CM-PCR) as a semiquantitative assay of gene dosage. PLP gene duplications were identified in four families by CM-PCR and confirmed in three families by densitometric RFLP analysis. Because a homologous myelin protein gene, PMP22, is duplicated in the majority of patients with Charcot-Marie-Tooth 1A, PLP gene overdosage may be a important genetic abnormality in PMD and affect myelin formation.

Effect of carnitine administration on glycine metabolism in patients with isovaleric acidemia: significance of acetylcarnitine determination to estimate the proper carnitine dose

In isovaleric acidemia (IVA), accumulated isovaleryl-CoA in the mitochondrion induces variable metabolic disturbances. To remove intramitochondrial isovaleryl groups, glycine therapy has been advocated primarily. On the other hand, secondary carnitine deficiency has been documented in this disorder and carnitine supplementation alone has been reported to be effective. In the present study, we administered carnitine and glycine to patients with IVA, and investigated serum carnitine and urinary excretion of total and free carnitine, acylcarnitine profile (i.e., isovalerylcarnitine and acetylcarnitine), and isovalerylglycine. By adding carnitine to glycine supplementation, more isovalerylglycine, not only isovalerylcarnitine, was excreted in the urine. Acetylcarnitine was detected in the urine only when sufficient carnitine was supplemented. We concluded that combined therapy of glycine and carnitine is more effective and safer to eliminate isovaleryl-CoA in IVA than conventional therapy using either glycine or carnitine. Urinary acetylcarnitine concentration might be a good marker indicating the optimal dose of L-carnitine supplementation.

Secondary carnitine palmitoyltransferase deficiency in chronic renal failure and secondary hyperparathyroidism

A 14-year-old girl, having mental and growth retardation with end stage renal disease, was affected by a stroke-like attack. The attack was associated with transient low density areas at both sides of the parietal portion on head CT. Lactic acidosis, hypertrophic cardiomyopathy, angina pectoris-like attacks, hypertension and hyperparathyroidism were also observed and they were supposedly due to mitochondrial cytopathy. No morphological or biochemical abnormalities were found on the mitochondrial respiratory chain. However, muscle carnitine palmitoyltransferase (CPT) activity was significantly low, which was restored to a normal level after hyperparathyroidism was controlled by alphacalcidol administration. Furthermore, we also found two more chronic renal failure patients with secondary hyperparathyroidism, as well as the primary hyperparathyroidism patient showing markedly low muscle CPT activity. These findings suggest the possible contribution of parathyroid hormone to lipid metabolism in skeletal muscle and to the myopathic manifestations often seen in hyperparathyroidism.

Biochemical bases in differentiation of a mouse cell line GSM06 to gastric surface cells

A mouse gastric surface cell line GSM06 established from a transgenic mouse harboring temperature-sensitive simian virus 40 large T-antigen gene was subjected to the lipid and glycoprotein analysis. When GSM06 cells were cultured for a long time after formation of a confluent monolayer, they differentiated to resemble foveolar epithelial cells morphologically. Biochemical changes during culture were studied in cells harvested just when a monolayer had formed (day 0), on day 7, and on day 21. Content of total phospholipids, cholesterol, cholesterol sulfate, total sugar and sialic acid increased about 1.5-fold from day 0 to 7 and remained elevated till day 21. The fatty acid composition of phospholipids revealed increased relative levels of oleic acid in phosphatidylcholine and phosphatidylethanolamine, and an increased level of plasmenylethanolamine from day 0 to 7. The level of dolichylphosphate continued to increase in a time-dependent manner. Glycosylation of various proteins, detected with lectins, was enhanced from day 7. In addition, greater resistance to taurodeoxycholate and acetylsalicylic acid was observed on days 7 and 21 than on day 0. Thus, enhanced glycosylation of proteins and an overall increase in the area of cellular membranes were the major changes in GSM06 cells during culture, and they were accompanied by an enhancement of cytoprotective potential.

Direct evidence of the production of IgA by tonsillar lymphocytes and the binding of IgA to the glomerular mesangium of IgA nephropathy patients

Tonsils were obtained by tonsillectomy from a 33-year-old woman with IgA nephropathy. Hetero-hybridoma cells of human tonsillar B-lymphocytes with mouse myeloma cells (NS-1) were made, and cultured in HAT medium supplemented with 10% fetus bovine serum and hybridoma cloning factor. The culture medium was analyzed by Western blot analysis using anti-human IgA antibody, and both IgA1 and IgA2 were demonstrated to be produced. The specimens of the biopsied kidney tissue of IgA nephropathy were washed with 0.02 M citrate buffer (pH 3.2) to remove deposited IgA from glomerulus. The specimens were then incubated with the culture media of hybridoma cells, and immuno-fluorescence analysis using FITC-conjugated anti-human IgA antibody was performed. IgA deposit was efficiently removed by washing with citrate buffer and was recovered after incubation with the culture medium of hybridoma cells. Direct evidence of binding of IgA produced by tonsillar B-lymphocytes to the glomerular mesangium of IgA nephropathy was demonstrated.